Research Of Micro-soale Fluid Based On Lattice Boltzmann Method

As an emerging intersect subject, the micro-scale fluidics has been widely used in micro and nano-electromechanical systems, micro total analysis system, biochips, aerospace and other fields. The microfluidic driving and controlling technique with small dose, high accuracy and high flexibility, are the critical technologies in the microfluidic system; controlling the temperature strictly plays a vital role in the whole system, and the effect of the heat transfer is indispensable. As the scale of the systems decreases, the effects which were neglected in the macro-field play an important role in micro-scale flow. Therefore, the traditional macro-driven approach and the research about the heat transfer were not suitable for the micro-fluidics. On the other side, because of the micro-scale flow discontinuity, the classical fluid dynamics method based on the assumption of continuous media is no longer suitable. And, the molecular dynamics is difficult to get extensive application due to the huge computational cost. However, as a mesoscopic scale method, the kinetic-based lattice Boltzmann method with its certain advantages such as high numerical efficient, easy to implement, parallel algorithms, has been a powerful numerical technique for simulating micro-scale fluid flows.Given this, this paper employed the lattice Boltzmann method to research the microfluidic driving and the heat transfer. The numerical study of these two problems requires powerful capabilities to handle the complex moving boundary and the non-isothermal flow. However, the lattice Boltzmann method has some shortcomings in these areas:when handing the complex moving boundary, the Immersed Boundary-lattice Boltzmann method needs to transform the structure variation of moving object into the deformation force, which would increase the computational cost; on the other hand, most of the existing thermal lattice Boltzmann method are "decoupling" models, i.e. the change of temperature could not influence the velocity field, which causes these models to be limited to Boussinesq flows. Based on these problems, this paper studied the problems of the micro-fluidic driving and the heat transfer. The idiographic work is as follows:1. When using the traditional Immersed Boundary-lattice Boltzmann method to handling the complex moving boundary, the transformation between the variation of the immersed boundary and the magnitude of force leads to the complex calculation and high computational cost. Due to the deformation information all contains in the traveling wave, this article proposed to introduce immersed moving boundary into lattice Boltzmann equation as velocity source and built a modified Immersed Boundary-lattice Boltzmann method. We used this method to handing the bio-inspired traveling wave micro pump. This paper build a novel bio-inspired traveling wave micro pump based on the movement pattern of the sperm. A flexible elastomer with one end fixed is placed in the micro-channel, and the moving of the fluid is driven by the traveling-wave deformations on the elastomer. This method improved the computational efficiency and the accuracy because of the procedure simplicity. To validate the present method, simulations of different methods including the conventional IB-LBM and the finite-difference methods were made. Numerical-simulation experiments were carried out to discuss the effect of the traveling-wave deformations on the pressure distribution and velocity field and to probe the effects of frequency, amplitude, elastomer’s length, wavelength, the position of elastomer, and kinematic viscosity of the fluid on the flow rate.2. Because most of the existing thermal lattice Boltzmann methods are "decoupling" models, i.e. the change of temperature could not influence the velocity field, this paper proposed a coupling double-distribution-function thermal lattice Boltzmann method which introduced the temperature change into the lattice Boltzmann momentum equation in the form of the momentum source to realize the coupling between the momentum field and the energy field. This method could consider the effect of viscous dissipation and compression work on the microfluidics. This paper verified the feasibility and accuracy of this method by numerically simulation of the micro-scale natural convective heat transfer, and analyzed the effect of the effect of viscous dissipation and compression work on the temperature, velocity and the averaged Nusselt number at different Rayleigh number and Prandtl number.3. This paper studied the effect of viscous dissipation and compression work on the micro-scale Rayleigh-Benard convection employing the coupling double-distribution-function thermal lattice Boltzmann method. The temperature distribution, the flow distribution and the average Nusselt number at different Rayleigh number and the aspect ratio were used to analyze the effect of the viscous dissipation and compression work on the micro-scale Rayleigh-Benard convection. The study found that:the effect of viscous dissipation and pressure work can promote the convection heat transfer, and this promotion can enhance with the increase of Rayleigh number; as the size of the model decreases, the number of the eddy increased exponentially and the shape of the eddy also changed in the model considering viscous dissipation and compression work.